Microsoft Word - QAS-TB3.DOC

Quality-Assuring Scheduling (QAS) has been invented to provide statistical guarantees to real-time applications with variable execution times scheduled in a reservation-based fixed-priority system. The admission control is based on a probabilistic model to ensure that a requested percentage of jobs of a periodic application is successfully executed over a longer time span even in permanent overload situations. However, the original approach is restricted to task sets with uniform periods and using nonpreemptible resources. This work overcomes these limitations. Now we extend the QAS admission algorithm to support task sets with harmonic and arbitrary periods. Our evaluation of the presented admission models shows the nearly full compliance of the predicted qualities with both simulations and measurements using a prototype real-time system.